/* testpwrite.c
 * reproduces issue on NFS 4.2 client on Linux 5.10.5
 * (c) Kurt Garloff <scs@garloff.de>, 1/2021
 * License: GNU GPL 2 or later 
 */

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <time.h>

#define MAXBUF 1048576
#define MAXSIZE (128*MAXBUF)
#define REP 16384

long randomwrite(int fd)
{
	void* buf = malloc(MAXBUF);
	long written = 0;
	int rep = REP;
	int ret;
	if (!buf) {
		perror("malloc");
		return -3;
	}

	memset(buf, 0, MAXBUF);
	while (--rep) {
#if MAXSIZE >= RAND_MAX
		loff_t offset = rand() * (MAXSIZE/RAND_MAX);
#else
		loff_t offset = rand() / (RAND_MAX/MAXSIZE);
#endif
#if MAXBUF >= RAND_MAX
		size_t len = rand() * (MAXBUF/RAND_MAX);
#else
		size_t len = rand() / (RAND_MAX/MAXBUF);
#endif
		//ret = pread(fd, buf+len/4, len/2, offset);
		/* Slowly fill in some random non-0 values */
		*(int*)(buf + (len - len%8)) = rand();
		ret = pwrite(fd, buf, len, offset);
		if (ret < 0) {
			fprintf(stderr, "pwrite(%i,%p,%li,%li): ", fd, buf, len, offset);
			perror("");
			return -1;
		} else 
			written += ret;
	}
	return written;
}

int main(int argc, char *argv[])
{
	srand(time(0));
	int fd = open("testfile", O_RDWR|O_CREAT, S_IRUSR|S_IWUSR|S_IRGRP);
	if (fd <= 0) {
		perror("open(\"testfile\")");
		return 2;
	}
	ftruncate(fd, MAXSIZE);
	unlink("testfile");
	long rc = randomwrite(fd);
	close(fd);
	if (rc < 0)
		return -rc;
	printf("%li bytes written successfully\n", rc);
	return 0;
}